Material and method for radiography



Patented Nov. 17, 1942 MATERIAL AND METHOD FOR RADIOGRAPHY Charles Pecher, Berkeley, Calif., assignor to Re:-

search Corporation, New York, N. Y., a corporation of New York N 0 Drawing.

4 Claims.

My invention relates to radiography and more particularly to a radioactive material ideally adapted .for the commercial production of industrial radiographs.

Among the objects of my invention are: to produce a material suitable as a radiation source for radiography having a half-life cycle completely satisfactory for commercial use; to provide a radioactive material having a substantially monochromatic gamma-radiation; to provide a radioactive material emitting a hard, substantially monochromatic gamma-radiation, with almost no beta-radiation; to provide a method of producing industrial radiographs of metal objects; to provide a radiation source of relatively small bulk; and to" provide an easily handled, relatively safe, and efficient source of hard gamma rays.

. It has long been known that radium may be used as a source of radiation to produce radio-- graphs of metal objects. Radium, however, has a number of disadvantages when used as asource of radiation for use in radiography. Radium is relatively expensive. Radium is dangerous to handle because of the wide band of alpha, beta, and gamma-radiation 'emitted therefrom. Radium also has a relatively long half-life. .This

material, therefore, in its useful form has con siderable bulk in quantities sufiicient to produce satisfactory commercial radiographs of metal objects, and consequently cannot closely approach a point source.

It will be obvious that the greater the bulk or volume of the source of radiations, the more diflicult it will be to produce satisfactory radiographs having high definition, particularly through bulky objects such as castings, motors, and the like.

It should also be pointed out that the mere fact that radium does have a long half-life period, means that individual useful units thereof are intrinsically expensive, must be carefully guarded to prevent loss, and require costly insurance protection.

The half-life of radon is very short. Its use as a radiographic source requires that a source of radium be closely and quickly available. Furthermore, considerable apparatus and labor are required to prepare radon seeds.

Broadly, my invention comprises the production and use as a radiation source for radiovgraphs, of a radioactive material such as, for

example, radioactive yttrium 86, which has a half-life of about 100 days. Such a half-life has been found to be of sufilcient length to make the Application May 1 941, v H Serial N0. 393,416 i I material commercially useful for the production of radiographs, yet this life is sufficiently short so that the loss of any individual unit quantity of the material is not vital either from the point.

of view of. expense orof danger, 'as the material loses its power within a reasonable time.

iv cyclotron is dissolved in I-ICl.

Furthermore, I have found that radioactive yttrium emits a substantially monochromatic hard gamma-radiation having 'an energy value of about 1.9:.1 million electron volts with prac- 'tically no beta-radiation harder than 300 thou-.

sand electron volts (k. e. v.). The gamma-ray absorption curves in copper, lead, and iron, of radioactive yttrium, and radium C when filtered through 2 cm. of lead are almost identical. There are no radioactive gaseous emanations suchas radon from radioactive yttrium. f v 7 Due to'the fact that the gamma-radiation is. substantially monochromatic and hard, andthat the same radiation intensities can be obtained from much smaller volumes, radioactive yttrium is a better source than radium, of radiations to be utilized for the purpose of producing industrial radiographs. Due to the important differences as set forth herein, it cannot be considered that radium and radioactive yttrium are'equivalents for radiography.

In the production of radioactive yttrium 86 in accordance with my invention,'strontium is bombarded as, for example, with 16-million-volt deuterons. Among others, two important materials are produced: first, radioactive strontium, which is in demand for biological and therapeutic investigations; and second, radioactive yttrium is also produced. I have separated such radioactive yttrium from the radioactive strontium. The strontium may then be utilized for its useful purposes.

The bombarded strontium, coming from the The radioactive yttrium is then precipitated as hydroxide in the presence of a carrier which may be inactive yttrium, but preferably an aluminum, iron, or copper salt. The radioactive yttrium may then be separated from the carrier by the standard ether process, for example, when the carrier is an iron salt. After separation the radioactive material may be introduced into a seed capsule of glass or meta1 of minimum practical size. When only small quantities of radioactive yttrium are available, some portion of the carrier may be left for ease of handling, but with larger quantities comphere separation may be made.

As to yield. An amount of radioactive yttrium 86 giving a hard gamma-ray intensity equal to 12 milligrams of radium is produced when strontium is bombarded for approximately 1,000 microampere hours With lfi-million-volt deuterons. Inasmuch as there is a demand for large quan tities of radioactive strontium for therapeutic purposes, I am able to segregate and make available for radiographic purposes a relatively large amount of approximately IOO-day radioactive yttrium.

I have found, for example, that satisfactory radiographs of thick metal objects may be taken through 2 inches of iron using as a source, an amount of radioactive yttrium corresponding in gamma-ray production to 15 milligrams of radium, with an exposure, for example, of 5 hours, at 6 inches from an X-ray film. Large. amounts of radioactive yttrium will, of course, give radio graphs with shorter exposures. Excellent definition is obtained because of the fact that the volume of radioactive yttrium 86 is much smaller than the bulk. of radium needed to produce the same gamma-ray intensity,

The intensity of the gamma-radiation from the radioactive yttrium may be increased several hundred times without appreciably increasing the minimum practical size of the seed capsule, as

the effective volume of radioactive, yttrium is several thousand times smaller than the amount of radium giving the same gamma-ray intensity.

For example, it would be impossible to produce a satisfactory definition in a radio'graph if 10 or 20 grams of radium were to be used as a radiation source, because the size of the material would be too large. However, a few milligrams of radioactive yttrium 86 will deliver the same gamma-ray intensity to give good definition because of. the much smaller bulk, and closer approach insurance on radioactive yttrium will be greatly reduced with respect to unit intensity, below the cost of a similar amount of radium. The halflife is sufiicient for the material to be produced by bombardment, shipped, and utilized commercially. The material can be produced as needed and regularly supplied to the users thereof.

Furthermore, the increasing use of radioactive yttrium 86 in industry for purposes of radiography will simultaneously cause the production of relatively large quantities of radioactive strontium, with consequent reduction in price and consequent increased availability for the medical profession.

Iclaim:

1. The method of producing industrial radiographs of relatively thick metal objects which comprises placing a radiation sensitive surface on one side of said object and exposing the other side of said object to the strong substantially monochromatic gamma-radiation from radioactive yttrium 86, produced by'deuteron bombardment of strontium compacted to a minimum practical source volume. V

2. In combination with a radiation sensitive surface and a metal object to be radiographed, a radiation source comprising gamma radioactive yttrium reduced by purification to a minimum practical source volume.

3. The method of producing an image which comprises exposing an object to the strong gamma-radiation of a compact mass of radioactive yttrium 86, reduced by purification to a minimum bulk capable of being handled in a practical manner, and intercepting said radiation after passing through said object to form said image.

4. The method of producing industrial radiographs of relatively thick metal objects which comprises mixing strongly gamma-radioactive yttrium with the minimum amount of carrier necessary for practical handling of said yttrium, irrespective of the amount of radioactive. yttrium, compacting said carrier and yttrium, exposing an object to the gamma-radiation of said com- :pacted material, and intercepting said radiation after passing through said object to form an image. I

CHARLES PECHER. 

